Theoretical calculations of pH at a cathodically polarized metal surface have received much attention in the literature. In 1965, Engell and Forchhammer, P. Corros. Sci., Vol. 5, p. 476 (1965), calculated the pH at the surface of cathodically polarized steel in sea water to be 10.9. In 1981, Wolfson and Hartt, Corrosion, Vol. 37, No. 2, p. 70 (1981), reported calculating the values of pH at the surface of cathodically polarized metals to be in the range of from about 10.0 to 11.25.
In 1974, Kobayashi, "Effect of Environmental Factors on Protective Potential of Steel", Proc. 5th Int. Cong. met. Corros. Tokyo, 1972. National Association of Corrosion Engineers, Houston, Tex., p. 629 (1974), experimentally measured the pH at a distance of 0.1 mm from the surface of an unstirred 3% solution of sodium chloride. In the experiment Kobayashi measured the pH of the bulk as 8.0 and the pH close to the metal surface as being 11.5.
Theoretical prediction of pH at a cathodically polarized metal surface is principally based on oxygen consumption and hydroxyl ion production rates. Oxygen consumption and hydroxyl ion production are not, however, the sole factors influencing pH at the metal-water interface. In addition, physical factors such as diffusion and convection as well as temperature, electrolyte velocity and electrolyte composition also affect interfacial conditions. The conditions at the metal-water interface are crucial for the effectiveness of cathodic protection systems. Since some physical factors may vary with time, effectiveness of cathodic protection may vary with time as well.